1. Field of the Invention
The present invention relates to a workpiece taking out robot system having a conversion-calculation function with regard to the position and orientation of a workpiece to be taken out by a robot, and a workpiece taking out method while executing the conversion-calculation.
2. Description of the Related Art
Generally, in a robot system for taking out a plurality of randomly located workpieces one-by-one by using a robot, the position and orientation (hereinafter, also referred to as “position/orientation”) of the workpiece are detected by a sensor, and a hand of the robot is moved to the detected position and orientation so as to hold and take out the workpiece. As a relevant prior art document, JP 2007-203406 A discloses a workpiece taking out device including: a robot configured to grip and take out a plurality of the same kind of workpieces located in a container; a robot controller for controlling the robot; a video camera positioned just above the container and configured to capture the workpieces in a wide range; and an image processor for processing an image obtained by the video camera.
JP 2008-272886 A discloses a device and a method, in which a candidate position of a workpiece gripped by a robot hand is automatically selected based on information of the shape of the workpiece, and a grip path is generated along which the robot hand approaches the workpiece based on the selected candidate position, in order to reduce time required for a teaching operation.
Further, JP H05-104465 A discloses an operation scheduling device for a robot, wherein: position/orientation candidates are calculated where an object can be gripped and located, based on initial and target states of the object and a geometrical feature of a robot hand; an opened pyramid is selected which does not interfere with an obstacle, among pyramids each having a center corresponding to a grip position of the calculated candidate; a distance between the selected opened pyramid and a closed pyramid is calculated; and the position/orientation candidate having the widest operation area for a grip operation is selected among the candidates, based on the calculation result.
In many cases, the sensor for detecting the position/orientation of each of the randomly located workpieces is positioned above the workpieces so that all of the workpieces can be detected. Therefore, a plurality of detection results can be obtained with respect to the located workpieces, and then a priority order of the workpieces to be taken out can be determined so that the robot can take out the workpieces according to the priority order. However, since such a process is carried out based on the result (an image) obtained by capturing the workpieces from above, when the uppermost workpiece cannot be taken out due to interference between the robot hand and the container, etc., another workpiece positioned immediately below the uppermost workpiece may also not be taken out due to the existence of the uppermost workpiece. As a result, the plurality of workpieces may remain in the container without being taken out (see FIGS. 4a to 6b as described below).
In order to resolve the above problem in the configurations of the above patent documents, a method for calculating the grip position based on a previously registered geometrical feature of a workpiece, or a method for matching a detected workpiece with a previously registered three-dimensional model of the workpiece can be used, whereby a portion of the workpiece can be specified so that the robot can grip the portion without interfering with an obstacle, etc. However, in such a method, it is necessary to previously register or store the three-dimensional model of the workpiece, which is labor intensive in particular when there are many kinds of workpieces.